An organic light emitting diode is formed of two opposite electrodes and thin films of organic materials having multilayered semiconductor properties existing therebetween. The organic light emitting diode of the above configuration uses a phenomenon where electric energy is converted into light energy by using an organic material, that is, an organic light emission phenomenon. In detail, in the structure where the organic material layer is disposed between the anode and the cathode, if a voltage is applied between two electrodes, holes are injected to the organic material layer in the anode and electrons are injected into the organic material layer in the cathode. The injected holes and the electrons meet each other to form an exciton, and the exciton is reduced to a bottom state to emit light.
In the above organic light emitting diode, light that is generated in the organic material layer is discharged through the light transmissive electrode, and the organic light emitting diode may be generally classified into a top emission type, a bottom emission type and a dual emission type. In the case of the top emission or bottom emission type, one of two electrodes should be a light transmissive electrode, and in the case of the dual emission type, all the two electrodes should be a light transmissive electrode.
In respect to the organic light emitting diode, many studies have been concentrated since Kodak, Co. Ltd. announced that in the case where the multilayer structure is used, driving at a low voltage is implemented, and recently, a natural color display using the organic light emitting diode is attached to a mobile phone and commercialized.
In addition, a study for the recent organic light emitting diode using a phosphorescent material instead of a known fluorescent material has been made, such that efficiency is rapidly improved, and it is expected that the diode would be able to replace a known lighting in the near future.
In order to use the organic light emitting diode as lighting, unlike a known natural color display, the diode should be driven at high brightness, and a constant brightness should be maintained like a known lighting. In order to sufficiently improve brightness of the organic light emitting diode, light emission should be implemented in a large area, and in order to implement light emission in the large area, a high driving current should be used. In addition, in order to maintain the constant brightness in the large area, the above high current should be uniformly injected into the diode having the large area.
In general, as the anode material of the organic light emitting diode, metal oxide having a large work function is mainly used. However, the electroconductivity of the metal oxide is not relatively high. Accordingly, in the case where the metal oxide is used in an organic EL or a LCD having a small display area, there is no problem, but in the case where the metal oxide is used in an organic EL having a large area for being used in lighting devices, a voltage decrease by a high current is large, such that the current is not uniformly injected into a light emission surface, and therefore light emission of the diode is not uniformly implemented. For example, in the electrode, light emission occurs only around a portion that is electrically connected to a driving circuit and weak light emission may occur or no light emission may occur in the remaining region.
Meanwhile, as the cathode material of the organic light emitting diode, the metal having the small work function or an alloy thereof is mainly used. The above metal may have the high electroconductivity, but in the case where transparency of the electrode is required because of characteristics of the organic light emitting diode, if the electrode is formed of a thin film, the electroconductivity is decreased. Accordingly, even in the above case, since the current is not uniformly injected into the light emission surface, light emission of the diode is not uniformly implemented.
Therefore, in order to use the organic light emitting diode as the lighting device, the light emission of high brightness needs to uniformly occur in the diode having the large area by decreasing resistance of the electrode.
In addition, the decrease of the resistance of the electrode may also be usefully used in manufacturing of the organic light emitting diode having the large area and a passive matrix display diode. Since the passive matrix display does not require an amorphous or poly-silicon thin film transistor back plate like an active matrix, a manufacturing cost is very low. However, recently, since the passive matrix organic EL display has various problems, an active matrix organic EL display rather than the passive matrix organic EL display is rising as a candidate for commercialization. One of the important problems of the passive matrix organic EL display is an essential technology for manufacturing an electrode having excellent light transmission and electroconductivity in manufacturing of the passive matrix organic EL display diode, but if resistance of the recently used electrode is large and the size of the display is increased by this, a voltage decrease in the electrode becomes serious, such that it is difficult to implement a display image.
Accordingly, in an organic light emitting diode field, development of a technology for decreasing resistance of the electrode is required.